Dissociation constants of phosphoric acid at 25°C and the ion pairing of sodium with orthophosphate ligands at 25°C

The first and second acidity constants of phosphoric acid were determined in a 0.70 ionic strength solution of both a sodium and a potassium ion background salt at 25°C. These experimentally determined constants were compared to literature values as well as values calculated from a theoretical model. Assuming negligible ion pairing of the phosphate ligand with the potassium ions, the stability constants of the NaHPO ₄ ^- and NaH₂PO ₄ ⁰ complexes were determined to be 1.3±0.3 and 0.49±0.07 (mol-L^–1), respectively. These constants were used to model the speciation of orthophosphate in a background of a sodium salt from pH 3 to 10.     

Etude des complexes sulfosalicylate de cuivre(III), nickel(II), cobalt(II) et uranyle(II) a l'aide d'une resine echangeuse de cations: Study of the sulphosalicylate complexes ofcopper(II), nickel(II), cobalt(II) and uranyl(II) by means of cation-exchange resins.

Study of the sulphosalicylate complexes of copper(II), nickel(II), cobalt(II) and uranyl(II) by means of cation-exchange resins.The conditional stability constants of the 1:1 complexes of the sulphosalicylate ions (L^3-) with copper(II), nickel(II), cobalt(II) and uranyl ions have been determined in a sodium perchlorate solution (0.1 M) and at various pH values by a cation-exchange method based on Schubert's procedure. The limits of application of the method are discussed. The variation with pH of the conditional stability constants can be explained by the existence of the complexes: CuH₂L, CuHL, CuL^-; NiH₂L⁺, NiHL, NiL^-; CoHL, CoL^-; UO₂H₂L⁺, UO₂HL, UO₂L^-, UO₂LOH^2-. The stability constants of these complexes are reported. Distribution diagrams of the various complexes of each element with pH and total concentration of sulphosalicylate parameters are given.     

Etude de la complexation des lanthanides trivalents par les isomères de l'acide diaminocyclohexanetétraacétique: Partie 2. Les Constantes d'Acidité et les Constantes de Formation des Complexes 1:1 avec l'Acide trans-1,4-Diaminocyclohexane-N,N,N′,N′-Tétraacétique

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 2. Acidity constants and formation constants of the 1:1 complexes of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid)Potentiometric measurements of the acidity constants of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (trans-1,4-DCTA) and of the stability constants of its 1:1 complexes with the trivalent lanthanides are reported for an ionic strength of 1 (KCl) at 25°C. The behaviour of this ligand is similar to that of monoaminodiacetic acids, suggesting that only one N(CH₂COO^?)₂ group participates in chelation. The selectivity of trans-1,4-DCTA for the lanthanides is better than that reported for the monoaminodiacetic acids.     

Effets de la nature de substituants sur les constantes d'acidité et les constantes de stabilité des complexes de quelques acides nitroso-5-barbituriques

The effects of substituents on the acidity constants and stability constants of complexes of some 5-nitrosobarbituric acids). The acidity constants of some 5-nitrosobarbituric acids (violuric acids) vary according to the degree of substitution and the nature of the substituent at the 1- and 3-positions of the pyrimidine ring. The value obtained at ionic strength 0.5 mol l^?1 made it possible to calculate the stability constants of simple complexes of divalent cations (Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Fe²⁺). Potentiometric titrations were applied.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction del'acide nitrique par quelques dioxydes de diphosphine

The distribution of nitric acid between an aqueous phase of constant or variable ionic strength and a benzene solution of diphosphine dioxide can be explained by the following reactions H⁺_a+ NO_3^-a+ DiPO₀ ? D1PO·HNO₃₀ H⁺_a+ NO_3^-a+ DiPO·HNO₃₀ ? DiPO·2 HNO₃₀ At constant ionic strength, the stability constants K₁″ were determined for the complexes 1,1-DiPO·HNO₃ (98 ± 01 (M)^-1), 1,4-DiPO·HNO₃(44±3 (M)_-1) and 1,5-DiPO·HNO₃ (51 ± 1 (M)^-1). The constants K₁₁″ for the complexes 1,1-DiPO·2 HNO₃ and 1,5-DiPO.2 HNO₃ are respectively 035±001 (M)^-1 and 62 ±0.05 (M)^-1 at 25°. With an aqueous phase of variable ionic strength, values of K₁'=54±7 (M)^-2 for 1,5-D1PO.HNO₃ and K_II'=65 ± 04 (M)^-2 for 1,5-DiPO·2 HN0₃ were obtained     

Etude de la complexation des lanthanides trivalents par les six isomeres de l'acide diaminocyclohexanetetraacetique: Partie 1: synthèses et détermination des constantes d'acidité et des constantes de formation des complexes 1:1 avec les lanthanides trivalents de l'acide trans-1,2-diaminocyclohexane-N,N,N′,N′-tétraacétique

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 1. Syntheses, acidity constants of trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, and formation constants of its 1:1 complexes.)The syntheses of five isomers (1,2 cis, 1,3 cis, 1,3 trans, 1,4 cis, 1,4 trans) of diaminocyclohexanetetraacetic acid which are not commercially available are described. For comparison with literature vlaues, potentiometric measurements of the acidity constants of the sixth isomer (1,2 trans) and of the stability constants of its 1:1 complexes with trivalent lanthanides are reported for an ionic strength of 1 (KCl) at 25°C. In contrast to some literature data, the stability constants found, plotted as a function of Z, display only one discontinuity at the level of gadolinium.     

Stability constants of iron(III)-8-hydroxyquinoline complexes

Spectrophotometric determination of the formation constants of iron(III)-8-hydroxyquinoline complexes in 0.1 M sodium perchlorate solution at 25° gave the values K₁=[FeOx²⁺]/([Fe³⁺][Ox^-])=4.9·10¹³, K₂=[FeOx₂⁺]/([FeOx²⁺][Ox^-])=4.2·10¹² and K₃=[FeOx₃]/([FeOx₂⁺][Ox^-])=3.9·10¹⁰. FeOx₂OH and FeOx(OH)₂ are obtainable as solid phases. FeOx₃ (K_sp=3·10^-44, intrinsic solubility 1.6·10^-7 M) dissolves in basic solutions to form FeOx₂(OH)₂ -In a solution saturated with FeOx³, ([FeOx₂(OH)₂^-][Ox^-])/[OH^-]²=7.7·10^-5.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine: Tome 1. l'extraction de l'acide nitrique par l'oxyde de tri-n-butylphosphine

The distribution of TBPO, water and nitric acid has been measured between an aqueous phase and various inert diluents at 25°. This study allowed the determination of the apparent stability constants for two molecular complexes, TBPO . HNO₃ (K₁=17.5±1.3 (M/l)^-2 (benzene); 20.1±0.8 (M/l)^-2 (toluene); II±2(M/l)^-2 (n-hexane) and TBPO . 2HNO₃.H₂O (K₂=(2.9±0.3) 10^-3(M/l)^-2 (benzene)).     

La matrice eau de mer et le signal du cuivre en spectrometrie d'adsorption atomique sans flamme : Partie 1: Etude de l'influence des principaux composants

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 1: study of the effects of principal inorganic ions.)The effects of the main inorganic ions of seawater (Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO^2?₄), and of nitrate as modifier, on the electrothermal atomic absorption spectrometric signal of copper are studied. Sodium chloride, sulfate or nitrate, magnesium chloride or nitrate, and calcium chloride can cause serious interferences. Thermal treatment at about 700°C prevents the interference of MgCl₂ by its hydrolysis. Ashing can be done without loss of copper at higher temperatures in the presence of sulfate salts (1300°C) and nitrate salts (1200°C) than in the presence of chloride salts (1100°C). This is ascribed to the stabilising effect of oxides and sulfides. A study of the influence of two-component matrices, MCl-MNO₃ or MCl-MSO₄, on the atomization signal of copper confirms this stabilizing effect which adds to the decrease in interference connected with removal of chloride in acidic medium.     

Ultraviolet-visible spectroscopic study of ion-pairs of sodium and potassium monoethyl benzeneazophosphonates and their crown ether complexes in acetonitrile

The u.v.-vis spectroscopic study of ion-pairs of the sodium and potassium monoethyl ester of [α-(4-benzeneazoanilino)-N-benzyl] phosphoric acid, [α-(4-benzeneazoanilino)-N-4-hydroxybenzyl] phosphonic acid and [α-(4-benzeneazoanilino)-N-4-methoxybenzyl] phosphonic acid and their complexes with dibenzo-18-crown-6 and dibenzo-24-crown-8 is described. While the free sodium salts of monoethyl benzeneazophosphonic acids, with an extremely low solubility in acetonitrile, may be classified as tight ion-pair salts, the correspondingly more soluble potassium salts exist as solvated loose ion-pairs in acetonitrile solutions. The interaction of crown ether either with sodium or potassium monoethyl benzeneazophosphonates produces crown separated ion-pairs.     

Constantes de formation des complexes de l'argent(I) avec differents ligands: Formation constants of silver(I) complexes with various ligands

Formation constants of silver(I) complexes with various ligandsThe various complexes AgL, AgL₂ and Ag₂L and the associated protonated or hydroxo complexes, formed between silver(I) ions and aminopolycarboxylic acids (DTPA, DCTA, EGTA, HEDTA, NTA), glutamic acid, α-alanine, diethylenetriamine and triethylenetetramine are described. Formation constants were calculated from potentiometric measurements with glass and silver electrodes at ionic strength 0.1 and 25°C.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine : L'extraction de L'acide nitrique par les oxydes de tri-n-hexylphosphine,de tri-cyclohexylphosphine et de tri-n-octylphosphine

The distribution of nitric acid between an aqueous phase and a solution of THPO, TcHPO and TOPO in benzene was measured at 25°. The apparent stability constants K₁' were found to be 17.2±1.0 (M)^-2 for THPO.HNO₃, 7.0±0.8 (M)^-2 for TcHPO.HNO₃ and 15.2 ± I.I (M)^-2 for TOPO.HNO3. The stoichionetry of the last complex was confirmed in n-octane solution at constant ionic strength in the aqueous phase.     

Étude thermodynamique de la complexation de l'argent par la pipérazine et quelques-uns de ses derives en milieu eau—ethanol

The stability constants of the complexes of Ag⁺ ion with piperazine and its 2-methyl-, 2-methyl-1-m-tolyl-, 2-methyl-1-p-tolyl- and 1-(p-methoxyphenyl)-2-methyl-derivatives are obtained at 25°C in water—ethanol (52%, w/w) solvent and KNO₃ 0.1 M ionic strength, by means of corresponding metal-complex electrodes.The enthalpies of formation are determined by direct calorimetry, in the same conditions of temperature and medium.The comparison of the thermodynamic functions ΔG_n°, ΔH_n°, ΔS_n° allows a discussion about the ability of each amine to coordinate, in terms of nature and position of the entering group.     

Complex formation equilibria of phosphocreatine with sodium,potassium and magnesium ions

The formation of complexes between phosphocreatine, H₂O₃PNHC(NH)N(CH₃)CH₂CO₂H, and the ions Na⁺, K⁺ and Mg²⁺ have been investigated under physiological conditions (aqueous solution, T=37 °C and I=0.25 mol dm⁻³) by means of ³¹P NMR spectroscopy. Only 1:1 complexes have been identified. Stability constants have been determined with the aid of the new computer program hypnmr-2000. log₁₀ K values were found to be−0.5(2),−0.3(2) and 1.43(3), respectively. The formation constant for the potassium complex is two orders of magnitude less that the literature value.     

Étude de la complexation des lanthanides trivalents par les six isomères de l'acide diaminocyclohexane-tétraacétique : Partie 3. Relation entre les Constantes d'Acidité et la Structure Moleculaire des Chélatants

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 3. Relationship between the acidity constants and the molecular structure of the ligands.)Potentiometric measurements of the acidity constants of the six isomers of diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) are reported for an ionic strength of 1 mol l^?1 (KCl) at 25°C. The values of the two constants K_a3 and K_a4 are correlated with the maximum N—N distance for each ligand. Ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) and some homologous ligands, including specially synthesized, 1,8-diaminooctane-N,N,N′,N′-tetraacetic acid and 1,10-diaminodecane-N,N,N′,N′-tetraacetic acid, are studied under the same conditions. It is proved that there is a relationship between the molecular structure and the affinity for protons.     

Solubilities of chromium(III) in molten potassium hydrogensulfate

The behavior of chromium(III) in molten potassium hydrogensulfate (220° C, P(H₂O) = 0.04 atm) is reported. Chromium(III) exists as Cr³⁺ in acidic medium, and as chromium(III) sulfate, which is insoluble in neutral medium but soluble in basic medium as Cr(SO₄)^?₂. The values of acidity constants and the solubilities of Cr(III) are reported.     

Stability constants of ytterbium cyclohexaphosphate complexes

The compositions of complexes formed in solution are calculated by the iteration (in three approximations) complex method and using the earlier study of the solubility in the YbCl₃-Li₆P₆O₁₈-H₂O system, in which one poorly soluble compound Yb₂P₆O₁₈ · 16H₂O and soluble ytterbium cyclohexaphosphate complexes are formed. The composition are [Yb₆(P₆O₁₈)]¹²⁺, [Yb₂(P₆O₁₈)]⁰, [Yb₃(P₆O₁₈)₂]^3?, [Yb(P₆O₁₈)]^3?, and [Yb₂(P₆O₁₈)₃]¹². The stability constants of these complexes are determined: β₆₁ = 1.2 × 10¹², β₂₁ = 6 × 10⁴, β₃₂ = 9 × 10¹², β₁₁ = 29.6, and β₂₃ = 3.9 × 10¹² at an ionic strength of ～1. The solubility product of Yb₂P₆O₁₈ · 16H₂O is found to be 2 × 10^?10. The curves of residual concentrations of ytterbium and cyclohexaphosphate plotted with reference to the stability constants of the complexes and the solubility product of Yb₂P₆O₁₈ · 16H₂O agree with experimental data.     

Enthalpic interactions of N-glycylglycine with xylitol in aqueous sodium chloride and potassium chloride solutions at T = 298.15 K

The mixing enthalpies of N-glycylglycine with xylitol and their respective enthalpies of dilution in aqueous sodium chloride and potassium chloride solutions have been determined by using flow-mix isothermal microcalorimetry at the temperature of 298.15 K. These experimental results have been used to determine the heterotactic enthalpic interaction coefficients (h_xy, h_xxy, and h_xyy) according to the McMillan–Mayer theory. It has been found that the heterotactic enthalpic pairwise interaction coefficients h_xy between N-glycylglycine and xylitol in aqueous sodium chloride and potassium chloride solutions are negative and become less negative with an increase in the molality of sodium chloride or potassium chloride. The results are discussed in terms of solute–solute and solute–solvent interactions.     

Calculations of microconstants and equilibrium formation constants for platinum(II) and palladium(II) halide complexes in solution

Distribution diagrams and formation functions for halide complexes [M(H₂O)_{4 ? n} Cl _n ]^{2 ? n} (M = Pt(II) or Pd(II)) and [PdCl_{4 ? n} Br _n ]^2? (n = 0?C4) in solution are analyzed in terms of the matrix model. Equilibrium constants for binding the first ligand $\left( {\bar K} \right)$ and corrections for the mutual influence between ligands (??) in the course of complex formation in solution are calculated. In examples analyzed, the substitution of chloride ion for water in the coordination sphere of platinum(II) and palladium(II) is an anti-cooperative process. The substitution of bromide ion for chloride ion in the coordination sphere of [PdCl₄]^2? is weakly cooperative. Quantum-chemical calculations show that platinum(II) and palladium(II) cis-bisaquadichloro complexes in the gas phase are thermodynamically less stable than trans-isomers. The cis-trans isomerization constants in the gas phase calculated by the DFT method and those found for solutions using the matrix model have the same order of magnitude.     

Dissociation constants for the zinc(II)-8-hydroxyquinoline complexes in aqueous and sodium dodecyl sulfate micellar solutions

The constants of dissociation of 8-hydroxyquinoline (pK ₁ and pK ₂) and of its complexation with zinc ions (logβ₁, logβ₂) in sodium nitrate aqueous solutions at 293 K were calculated by modeling potentiometric titration data. The values of logβ were obtained under conditions such that the complexes occurred simultaneously in the solution and at optimum values of the ionic strength and the ratio between the metal and ligand concentrations. The apparent constants of dissociation of 8-hydroxyquinoline and of its complexation with zinc ions in a 0.01 M sodium dodecyl sulfate solution were calculated. An increase in pK and logβ was explained by the stabilization of the different forms of the ligand and its complexes in the surfactant micellar phase.